Transcriptome dynamics at Arabidopsis graft junctions reveal an intertissue recognition mechanism that activates vascular regeneration. Transcriptome dynamics at Arabidopsis graft junctions reveal an intertissue recognition mechanism that activates vascular regeneration

The ability for cut tissues to join together and form a chimeric organism is a remarkable property of many plants, however, grafting is poorly characterized at the molecular level. To better understand this process we monitored genome-wide temporal and spatial gene expression changes in grafted Arabidopsis thaliana hypocotyls. Tissues above and below the graft rapidly developed an asymmetry such that many genes were more highly expressed on one side than the other. This asymmetry correlated with sugar responsive genes and we observed an accumulation of starch above the graft that decreased along with asymmetry once the sugar-transporting vascular tissues reconnected. Despite the initial starvation response below the graft, many genes associated with vascular formation were rapidly activated in grafted tissues but not in cut and separated tissues indicating that a recognition mechanism activated that was independent of functional vascular connections. Auxin which is transported cell-to-cell, had a rapidly elevated response that was symmetric, suggesting that auxin was perceived by the root within hours of tissue attachment to activate the vascular regeneration process. A subset of genes were expressed only in grafted tissues, indicating that wound healing proceeded via different mechanisms depending on the presence or absence of adjoining tissues. Such a recognition process could have broader relevance for tissue regeneration, inter-tissue communication and tissue fusion events. Overall design: We analyzed the poly-adenylated transcriptomes of Arabidopsis thaliana hypocotyle tissue during grafting. Our dataset contains 82 strand-specific samples, whereas each condition is represented by two biological replicates.

离体组织能够相互结合并形成嵌合有机体的能力，是许多植物的非凡特性之一，但目前人们对嫁接过程的分子层面机制仍知之甚少。为深入解析这一过程，本研究对嫁接后的拟南芥（Arabidopsis thaliana）下胚轴进行了全基因组范围的时空基因表达变化监测。嫁接位点上下的组织会快速形成不对称性，表现为大量基因在单侧的表达量显著高于另一侧。这种不对称性与糖应答基因的表达模式显著相关；研究人员观察到，嫁接位点上方的淀粉积累量会随糖转运维管组织重新连通后不对称性的减弱而逐步降低。尽管嫁接位点下方最初会出现饥饿应答，但嫁接组织中大量与维管形成相关的基因被快速激活，而在离体分离的组织中则无此现象，这表明存在一种不依赖功能性维管连接的识别机制被激活。作为细胞间转运的植物激素，生长素（Auxin）的应答反应会快速升高且呈现对称性，这表明在组织贴合后的数小时内，根系即可感知生长素信号，进而启动维管再生过程。存在一类基因仅在嫁接组织中表达，这表明伤口愈合的机制会因相邻组织是否存在而有所差异。这类识别过程对组织再生、组织间通讯以及组织融合事件均具有更广泛的研究意义。实验设计：本研究分析了嫁接过程中拟南芥下胚轴组织的多聚腺苷酸化转录组。本数据集包含82个链特异性样本，每个实验条件均设置2次生物学重复。